{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nN4BP1 functions as a versatile regulatory protein that modulates ubiquitin‐dependent signaling pathways. It directly interacts with E3 ubiquitin ligases such as Itch by binding to its WW domains, thereby competing with substrates like p73α, c‑Jun, and p63. This interaction inhibits substrate recruitment and subsequent ubiquitination, contributing to the stabilization of critical cell death regulators and potentially impacting tumor progression and chemosensitivity."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn immune cells, N4BP1 acts as a potent suppressor of inflammation. It limits cytokine production initiated by Toll‑like receptor (TLR) pathways, particularly those signaling via MyD88. However, following TLR3 or TLR4 stimulation as well as death receptor activation, caspase‑8 cleaves N4BP1, thereby relieving its inhibitory brake and permitting robust inflammatory responses."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nPost‑translational modifications further regulate N4BP1 function. It is subject to both polyubiquitylation, which targets it for proteasomal degradation, and SUMO conjugation, which can protect it from ubiquitin-mediated turnover. These modifications, together with its predominant nucleolar localization and dynamic accumulation at nuclear structures such as PML bodies, suggest that N4BP1 turnover is tightly controlled in response to cellular signaling cues."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its role in immune modulation, N4BP1 influences developmental and differentiation processes in nonimmune tissues. In the skin, high levels of N4BP1 restrict keratinocyte proliferation by binding to the mRNAs of AP‑1 transcription factors (JunB and FosB), thereby reducing their stability and curbing inflammatory cell recruitment—mechanisms that are critical to preventing psoriasis. In neural progenitors, N4BP1 negatively modulates Notch signaling by promoting the ubiquitin‑mediated degradation of the Notch intracellular domain (NICD), thus influencing the balance between stem cell maintenance and differentiation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nFurthermore, N4BP1 contributes to the fine-tuning of canonical NF‑κB signaling. By binding to NEMO—the signaling scaffold essential for IKK complex formation—and cooperating with noncanonical IκB kinases, N4BP1 limits the duration and intensity of NF‑κB activation and subsequent inflammatory gene transcription. This regulatory checkpoint ensures that immune responses do not become over‑exuberant."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": ""}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Andrew Oberst, Martina Malatesta, Rami I Aqeilan, et al. 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"}, {"type": "b", "children": [{"type": "t", "text": "N4BP1 negatively regulates NF-κB by binding and inhibiting NEMO oligomerization."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Nat Commun (2021)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1038/s41467-021-21711-5"}], "href": "https://doi.org/10.1038/s41467-021-21711-5"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "33654074"}], "href": "https://pubmed.ncbi.nlm.nih.gov/33654074"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "Prashant Sharma, Rodolfo Murillas, Huafeng Zhang, et al. "}, {"type": "b", "children": [{"type": "t", "text": "N4BP1 is a newly identified nucleolar protein that undergoes SUMO-regulated polyubiquitylation and proteasomal turnover at promyelocytic leukemia nuclear bodies."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Cell Sci (2010)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1242/jcs.060160"}], "href": "https://doi.org/10.1242/jcs.060160"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "20233849"}], "href": "https://pubmed.ncbi.nlm.nih.gov/20233849"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Chenliang Gou, Wenkai Ni, Panpan Ma, et al. 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